Conventional thinking suggests that the size of a vehicle is directly related to its safety. Bigger cars are safer, some say, while smaller cars lack the mass to protect occupants. But crash tests often disprove this, with some small cars performing better in controlled tests than larger vehicles. In recent testing by the Insurance Institute for Highway Safety (IIHS), half of small cars tested earned the institute's Top Safety Pick+ rating, its highest score. These tests included the new small overlap front crash test that IIHS introduced last year.

The new test simulates a frontal crash into a tree or utility pole. At 40 miles per hour, the vehicle impacts a barrier that covers just 25 percent of the width of the vehicle's front end, concentrating forces on a small area. IIHS assesses the damage and assigns one of four ratings: Good, Acceptable, Marginal or Poor. Only vehicles rated Good or Acceptable are eligible for a Top Safety Pick+ rating. Vehicles also must rate highly in IIHS's other four tests -- moderate overlap front, side, roof strength, and head restraints and seats -- to be named Top Safety Pick+.

While some performed better than others, the results illustrate that just because a vehicle is small doesn't mean it will not effectively protect occupants. IIHS chief research officer David Zuby echoed that sentiment.

"The small cars with marginal or poor ratings had some of the same structural and restraint system issues as other models we've tested," Zuby said. "In the worst cases safety cages collapsed, driver airbags moved sideways with unstable steering columns and the dummy's head hit the instrument panel. Side curtain airbags didn't deploy or didn't provide enough forward coverage to make a difference. All of this adds up to marginal or poor protection in a small overlap crash."

What it means to you: Be sure to consider safety ratings before making your next car-buying decision. While crash tests cannot simulate all the factors involved in a real crash, they can provide shoppers with a safety comparison for two or more models. The federal government rates safety and lists ratings on new-car window stickers. IIHS ratings offer shoppers a second opinion.

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